In general, to repair a defective pixel of a thin film transistor liquid crystal display (TFT LCD), a bright point of the pixel is often converted to a dark point or a gray point, but this pixel is still a permanent defective pixel.
FIG. 1 shows the conventional equivalent circuit of a pixel structure to explain the circuit of a TFT LCD. As shown in this figure, for a pixel, the gate electrode 410 electrically connects to a scan line 200, the source electrode 420 electrically connects to a data line 100 and the drain electrode 430 electrically connects to a pixel electrode 300.
FIG. 2 is the conventional equivalent circuit of a repaired pixel, which is repaired into a dark point. The drain electrode 430 of the pixel is shortened at a repair point 510 to electrically connect to a scan line 200. Since the pixel electrode 300 is electrically connected to the scan line 200 directly, the defective pixel shows a dark point.
FIG. 3 is the equivalent circuit of a repaired pixel, which is repaired into a gray point. The drain electrode 430 of the pixel is shortened at a repair point 520 to electrically connect to a data line 100. Since the pixel electrode 300 is electrically connected to the data line 100 directly, the defective pixel becomes a gray point.
However, the dark point or the gray point, which is still a defect of a TFT LCD, influences display performance. Furthermore, a bright point is a critical defect for a TFT LCD, so it is repaired into a dark point or a gray point. However, the display performance of a TFT LCD is still not significantly improved because of the permanent existence of a defective pixel. So, how to repair a defective pixel into a normal pixel and to prevent the defect is an important technique.